1. Field of the Invention
The present invention relates to a form measuring apparatus and a measurement method of finding a V groove center.
2. Description of Related Art
Scanning measurement by a coordinate measuring machine can be classified into autonomous scanning measurement, in which a scanning movement path is unknown, and nominal scanning measurement, in which a scanning movement path is known. Autonomous scanning measurement includes fixed height scanning measurement, which has as a condition that a center of a stylus tip of a scanning probe is confined to a constraint plane of a predetermined height. A scanning measuring apparatus performing fixed-height scanning measurement is disclosed in Japanese Patent Laid-open Publication No. 2005-345123, for example.
Meanwhile, Japanese Patent Laid-open Publication No. 2010-014638 discloses a V groove shape measuring method suitable for use when measuring a characteristic value (such as a pitch deviation or a diameter deviation) of a V groove formed in a spiral shape. In the V groove shape measuring method, a center of the V groove formed in the spiral shape on a work piece is found. A contra-approach direction vector perpendicular to a work piece center axis is found, and a probe is moved from a current position in an approach direction such that a stylus tip of the probe makes contact with one inclined surface of the V groove. Here, the approach direction is a direction opposite that of the contra-approach direction vector. Thereafter, the probe is moved such that the stylus tip scans along the inclined surface. When an angle created by the contra-approach direction vector and a probe normal line vector is within a predetermined value, a determination is made that the stylus tip is in a state of contact with two inclined surfaces of the V groove, and coordinate values for the stylus tip at that point are obtained as a measured value for the V groove center.